Welcome guest, is this your first visit? Create Account now to join.
  • Login:

Welcome to the NZ Hunting and Shooting Forums.

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed.

Alpine DPT


User Tag List

+ Reply to Thread
Results 1 to 1 of 1
  1. #1
    Member
    Join Date
    Mar 2012
    Location
    Waikato
    Posts
    1,934

    Scopes low light performance - link to scopecalc

    In the best internet tradition of linking rather than original contribution, this site scopecalc has a good explanation of factors affecting how well a telescopic sight will perform in twilight conditions. It has an online calculator which you can put your own figures into to illustrate and compare scopes.

    It explains why the capability of your own pupil to dilate can strongly affect how much benefit you'll get from a higher spec scope. Older people whose pupils can't dilate so far get less benefit from big objectives. Also why some brands like Swarovski quote smaller effective objective diameters at low power. No, its not just optical corner cutting - at powers below 5x, it really doesn't matter how big the objective is because the exit pupil is bigger than the human eye's pupil. They have a correction for "realistic light gain" which takes into account reduced resolution at higher magnification due to diffraction (bending of light around edges). I don't think "perceived brightness" is directly useful except for comfort but there is a table giving absolute illuminance values for common situations (bright sun, indoors, moonlight etc I would be interested to see what it is in NZ native bush under canopy) and relates these to the lower limit of high resolution colour vision in the human eye. Essentially, you need at least 3 - 10 lux at your pupil to see well enough to shoot. A 50mm objective can pull up full moonlight to this level at 8x but 32mm can't do it. Big objectives come into their own above 10x. Also, this shows that higher powers do give a brighter image. The idea of using low power for low light is just not right. I find I can see better in dark bush if I wind the power up and now a number says its true.

    Here's a comparison of my current scope and two contenders. The site has a cursor to give you numerical values across the graphs.


    Name:  PMIIZ5VX1.jpg
Views: 379
Size:  256.6 KB

    Here's the brightness table.

    Name:  PIlluminance.jpg
Views: 267
Size:  346.8 KB

 

 

Similar Threads

  1. Creating a link..
    By Pop Shot in forum Questions, Comments, Suggestions, Testing.
    Replies: 4
    Last Post: 29-11-2012, 11:29 PM
  2. Effect of suppressor on performance of a given load...
    By .22-250 everything in forum Firearms, Optics and Accessories
    Replies: 20
    Last Post: 11-07-2012, 05:51 PM
  3. .224 75gr Hornady BTHP - terminal performance
    By Beavis in forum Reloading and Ballistics
    Replies: 3
    Last Post: 28-06-2012, 08:24 PM
  4. 7mm 180 VLD Hybrid performance on game
    By leathel in forum Reloading and Ballistics
    Replies: 9
    Last Post: 22-05-2012, 07:03 PM

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
Welcome to NZ Hunting and Shooting Forums! We see you're new here, or arn't logged in. Create an account, and Login for full access including our FREE BUY and SELL section Register NOW!!